In general, spark plugs include an insulating sleeve having a central axial bore through which a center electrode extends. The insulating sleeve is positioned within and secured to a metal shell that serves as a mounting platform/interface to an internal combustion engine. The metal sleeve also supports a ground electrode that is positioned in a particular spaced relationship relative to the central electrode so as to define a spark gap. The spark plug is typically mounted to an engine cylinder head and selectively activated to deliver a spark that ignites a fuel/air mixture in an associated engine cylinder.
Smaller engines, particularly those employed in compact motor vehicles, have minimal available space for engine components. Cylinder spacing, i.e., the space between adjacent cylinders is also minimized to optimize engine size. As a result, spark plugs for smaller engines generally have a small diameter, e.g., in the range of 12 mm. Unfortunately, smaller diameter plugs have less available volume for internal components such as an insulator. As a result, insulator thickness must be reduced.